The lignoid compound asarinin and the insecticidal and sialogogic compound neoherculin were isolated earlier from the bark of Zanthoxylum clava-herculis L. (Rutaceae). In this study, the bark extract was found to be highly toxic to fish, and fractionation was undertaken based on this activity. After preliminary solvent partition and silica gel chromatography, five crystalline components (A-E) were isolated, with D and E responsible for the toxicity. Fractions A and B were identified as (-)-asarinin and (-)-sesamin (C₂₀H₁₈O₆, M⁺ 354), respectively. Fraction C (C₂₅H₂₈O₆, M⁺ 424) was a new lignoid compound assigned as γ,γ-dimethylallyl ether of (-)-pluviatilol (structure 5) via spectral data and stereochemical elucidation. Fraction D (C₁₆H₁₀NO₃), the major component, was neoherculin with an LC₅₀ of 2×10⁻⁷ M against Pimphales promelas. Fraction E (C₁₉H₁₇NO₃) was N-acetylanonaine, toxic to fish with an LC₅₀ of 3×10⁻⁴ M.